I am 27 years old, and I have written fanfiction for fifteen of those and it was only until maybe two years ago when I realized I can write whatever I want??? And it doesn't have to match canon or even make a single drop of sense?? I can write them off character too if I well so please?? Just for funsies? Because who's gonna stop me? The fandom police? People can be grouchy and angrily type till their fingers fall off that I'm wrong, and the characters are not like that, and the story is bad and still none of that will take away from my enjoyment of this mediocre 200k words fanservice crap I wrote for shits and giggles.
I'm always thankful when other people like my stories and it brightens my day to get good reviews and I'm not about to start writing fucked up offensive shit, but I'm just saying, if I want to write a 200k word fanfiction about a kids show and age them up to their 20's because I wanna see these two hot characters bang like their life depends on it, where the only thing smaller than the plot is my acknowledgment of canon personalities and questionable timeline, who's gonna stop me?
Just let people like what they like, my guy. That's why fics exist in the first place, otherwise we'd all just read the book, close it and move on with our lives.